This invention relates generally to apparatus and methods for measuring the absorptance of materials displaying reflecting and transmitting characteristics, and more specifically relates to the measurement of such characteristics by means of an integrating sphere.
In numerous applications of optical technology, it is of interest to establish the absorptance characteristics of samples of material of the type displaying both reflecting and transmitting characteristics. By the term "absorptance" is meant the quantity [1-(R.sub.s +T.sub.s ], where R.sub.s is the reflectance, and T.sub.s is the transmittance of the said sample. The indicated parameter, i.e., absorptance, may, for example, be of interest in connection with evaluation of samples of greenhouse glass, and of glasses and other materials used with solar cells.
To the extent the prior art has been concerned with evaluating optical characteristics of materials of the foregoing type, such art has dealt primarily with the reflectance of such materials. Various instrumentalities have thus been used for such purposes, including integrating spheres -- which indeed have long been known for use in evaluating the reflectance characteristics of all types of materials. Reference may usefully be had in this connection, to such articles as D. K. Edwards et al., "Integrating Sphere for Imperfectly Diffuse Samples" 51 Applied Optics 1279 (November, 1961); and to David G. Goebel, "Generalized Integrating Sphere Theory;" 6 Applied Optics 125 (January, 1967).
While instruments and techniques are also known which are useful in measuring transmittance of samples of the type cited above, in general such prior art (particularly where contemplating the measurement of absolute absorptance) has required two sequential steps of observations. Thus, where use of an integrating sphere has been contemplated, some type of displacement of the integrating sphere, or of the supporting structure between measurements, is commonly prescribed. Further, the integration or summations then performed were commonly enabled through the use of computers, or via other burdensome and costly techniques.
In accordance with the foregoing, it may be regarded as an object of the present invention, to provide apparatus and methods enabling rapid and economical measurement of the absorptance of reflecting and transmitting samples of material.